This is an in depth guide on how to beat pokemon yellow version. Well at least up until Brock at least ill have more on it later.
Pallet Town
(You're in your bedroom) Go to the computer and
access your PC, get the potion and get downstairs. Go outside, now go to
the very north, you should see some grass looking areas, go onto it, before
you get far, Prof. Oak will stop you and
lead you to his lab. Here you will receive your first
Pokemon,
Pikachu!
Before you get out of the lab, Gary will challenge you to your first match.
If you win, you get some money, if you lose, Gary gets the bragging rights.
One more thing, Pikachu will grow to level 6 if you win.
Route 1
Now that you have a Pokemon, go on to the bush in
the north and find fights, get Pikachu up to level 10. If Pikachu faints
(make sure that it doesn't, run from battles if you need to), you'll be
back in your house, talk to your mom and go back onto route 1. Make your
way through the route, talk to anybody you see, one guy will give you a
free potion, another will tell you a "faster" way to get home.
Viridian City
Go directly up and right to that first building
(with a "poke" sign on it) and go inside, go up and talk to the nurse behind
the counter she'll offer to heal your Pokemon, select heal. Now go northeast
to the pokemart (with a "mart" sign), you'll receive Prof. Oak's Parcel.
Go back to Pallet town, picking fights as you go (get Pikachu up to level
11).
Pallet Town
Go back into Oak's lab and talk to him, he'll give
you and Gary each a pokedex. Now go into Gary's
house and get a towns map, despite what Gary said, his sister will still
give you a map.
Route 1
Now get Pikachu up to level 12. Go into Viridian
City.
Viridian City
Now heal your Pokemon. Get a potion and 6 pokeballs
at the pokemart, you'll need them later. Go back to route 1.
Route 1
Capture a Pidgey and raise it to level 10, capture
a Rattata and raise it to level 7 (it should have learned quick attack).
Your Pokemon should be around level 12 or above, above would be great.
Go back to Viridian City.
Route 2
Switch your Pidgey as your leading Pokemon. Now
go north into Viridian Forest. (Don't forget to heal your Pokemon at the
Viridian poke center first)
Viridian City
Go to the poke center and heal your Pokemon, go
up and stop when you see an old man. Go left and you'll see a broccoli
like bush. Press A and you'll find a secret potion. Now go north to the
Viridian Forest.
Viridian Forest (Pokemon catching spree)
Now with a level 10 Pidgey leading, Pikachu at level
13, and a level 8 Rattata (you won't be using this much, only to catch
some Pokemon) you're ready for the forest. Immediately go up and
turn right into that bush of grass. Now you can find the caterpillar Pokemon
Caterpie. Use this chance to build up your other Pokemon. Fight with
a Caterpie until level 12 (it'll evolve twice). The final evolution of
Caterpie is Butterfree, his psychic attack Confusion will be a big help
soon! Remember to go back to Viridian City if you need medical help.
Getting through the forest
At the entrance, head northwest to find a pokeball. Go back to the
entrance and go right again, follow the path to find a bug catcher trainer;
it should be no problem if you have a level 12 Butterfree and a 12 Pidgey.
Go up the grass bush, you'll be challenged by another bug trainer. Go up
and get the potion, remember if your monster have fainted or has really
bad/low health (what I mean by bad is situations like poisoned, etc.),
go back to the Viridian City poke center. Use potions and antidotes only
if you really must. Keep on going; follow the road as it zigzags through
the forest. Keep on going until you reach another fork in the road, you
should be facing south when you encounter it. Go right and down to find
another potion. From there make your way to the northwest. There's another
bug trainer in your way but it's nothing you can't handle. Go north and
exit.
Pewter City
Instead of going to Brock, go heal your Pokemon
and go back to Viridian City instead, and from there, make your way west
of town.
Route 22
This is a great place to capture new Pokemon.
Don't miss both Nidorans, Spearow, and especially Mankey. If you go to
far you will run into...
Gary
I missed Gary here my first trip, he has added a
Spearow to his lineup since your last battle. Note: the outcome
of these first two battles determines how Gary will later on Evolve his
Eevee. If you beat him both times he will have a Jolteon, If you
win the first battle but lose this one he will have a Flareon, and if you
lose both he will evolve Eevee into a Vaporeon.
Route 23
The guard at the gate won't let you through, so
let’s get the badges shall we? Go back through the forest to Pewter City.
Pewter City
Heal your Pokemon. Now put Butterfree in front and
head into the pewter city gym. Brock will give you the Boulder Badge and
TM 34, which teaches bide (I wouldn’t use this, I’d just sell it).
After you finish Brock, go and buy 4 or 5 pokeballs at the pokemart. Heal
your Pokemon and head northwest to the museum. Talk to everyone, you'll
be able to fix the clues together later. Go right from the entrance to
the museum and you'll find another bush looking thing, cut it later when
you get HM 01 and go inside, you'll find a scientist who will give you
Old Amber. Oh, 1 more thing, get an escape rope; you'll need it pretty
soon.
Brock
Brock has a level 10 Geodude and a level 12 Onix,
Butterfree should go all the way with Harden and the Confusion attack,
but have a Nidoran or Mankey backing him up just incase. Don't even
think about using Pikachu...trust me.